Method of making a composite article



1963 w. F- BOHM ETAL 4 ,5

METg-IOD OF MAKING A COMPOSITE ARTI LE-j Filed Sept. 25. "1950 III/11 mmvms ZZ/a/Zaz ffladm 9 BY 6302429 .& A a/Zazz fig 7 @ggw TOE NE Y United States Patent Ofiice 3,ll2,5dl Patented Dec. 3, 1953 This invention relates to a method of making composite articles in which different metals are cast sequentially against one another in a firm and intimate bonding relationship, and more particularly to a method in which different metals having different coefficients of thermal expansion and different melting temperatures are cast in firm interlocking relationship.

It has been recognized in the past that the light weight and hi h thermal conductivity of metals such as aluminum and magnesium may be advantageously combined with the high wear resistance of ferrous metals such as cast iron in the manufacture of brake drums, automobile engine cylinders and the like. The objective in these composite structures is to employ the ferrous metal as the wear surface and to back it up with a body of a light metal such as aluminum having a high coefficient of thermal conductivity to effect a rapid dissipation of heat from the wear surface against which a piston or brake shoe may operate. A basic problem in the manufacture of such structures is that aluminum, for example, has a coefficient of expansion which is about five times that of iron so that on subjecting the composite structure to heat such as may be generated in a brake assembly or cylinder liner, the aluminum tends to draw away from the ferrous member to permit the formation of an insulating layer of air between the members so that the purpose for applying the aluminum body to the ferrous body is defeated.

It is a basic object of this invention to provide a composite metal structure in which different metals having different melting temperatures and coefficients of expansion are cast against one another in a firm and intimately bonded relationship. It is a further object of this invention to provide a composite metal structure in which a light weight metal having a relatively low melting ternerature and a high heat conductivity such as aluminum is cast against a metal having a relatively high melting temperature and high wear resistance such as cast iron to form a firm mechanical bond between the metals. It is another object of this invention to provide a process for casting a composite article composed of different metals having difierent melting temperatures in which a higher melting temperature portion is cast to a plurality of projections on a surface thereof, and thereafter the lower melting temperature portion is cast about these projections to form a mechanical lock between the cast bodies. It is still another object of this invention to cast a metal article having a plurality of protuberances thereon which have enlarged end portions and which may have another metal cast thereabout in interlocking relationship.

These and other objects are accomplished by casting a light metal body such as aluminum against a ferrous metal body in interlocking relationship. This is accomplished by first making a pattern in the shape of the ferrous metal body to be cast. Next, the portion of the pattern corresponding to the surface of the ferrous metal body against which the aluminum body is to be cast is coated with a light film of oil or similar relatively viscous, lightly sticky liquid. Beads of a porous synthetic resin such as expanded polystyrene are then dispersed over the oiled surface to which they adhere lightly. The pattern including the polystyrene beads adher ng thereto is then placed in a foundry flask in a conventional manner and a foundry sand impression is formed. The pattern is then withdrawn from the sand and as a result, the beads which were adhering lightly to the pattern are embedded in the surface of the resulting mold cavity of the sand impression. The mold is then closed and the ferrous metal poured in the conventional manner. The molten iron flows adjacent the embedded porous plastic, causes it to volatilize and burn out, and occupies the resulting voids. The resulting casting consists of a ferrous metal body having a beaded surface. Finally, the desired aluminum body is cast against the beaded surface whereby the aluminum metal flows about the bead portions of the ferrous metal casting and causes the aluminum body to be mechanically fastened to the ferrous metal body. A brake drum consisting of a cast iron liner and an aluminum heat-radiating drum or a cylinder composed of a ferrous metal liner and a finned heat-radiating body may be manufactured by this process.

Other objects and advantages of this invention will appear from the following description of a preferred embodiment of the invention, reference being made to the accompanying drawings, in which:

FIGURE 1 is a fragmentary cross-sectional view of a pattern of a cast iron liner of an automobile brake drum assembly;

FIGURE 2 is the pattern of plurality of porous plastic surface thereof;

FIGURE 3 is a fragmentary cross-sectional view of the beaded pattern of FlGURE 2 embedded in a foundry flask;

FIGURE 4 is a fragmentary cross-sectional View of the flask of FIGURE 3 with the pattern removed and the plastic beads embedded in a wall of the mold;

FIGURE 5 is a fragmentary cross-sectional view of a liner cast in a mold of FIGURE 4 having on its surface a plurality of protuberances;

FIGURE 6 is a fragmentary cross-sectional view of a foundry flask showing the liner of FIGURE 5 positioned therein; and

FIGURE 7 is a fragmentary cross-sectional view of an automobile brake drum assembly cast in the mold shown in FIGURE 6.

The invention will be described in detail in terms of a brake drum assembly for use in automobiles and the like. This brake drum consists generally of a cast iron liner having on the outer surfaces thereof a plurality of partially spherical beads integrally attached to the cast iron surface and an aluminum high heat conductivity body cast about the outer periphery thereof. The alumi num body is cast about the cast iron liner and about the bead-like protuberances of the cast iron body and is thereby strongly attached thereto. As a consequence, the aluminum body will remain in close contact with the cast iron liner regardless of the fact that in operation the temperature of the cast iron liner and the aluminum drum will vary over a considerable temperature range and the fact that the aluminum will expand at a rate several times that of the cast iron.

Referring to FIGURE 1 of the drawings, the process of this invention involves first making a smooth surfaced pattern It! in the form of the iron liner to be cast. This pattern may be made of wood, a synthetic resin such as polystyrene or a metal as is well known in the art. The outer surfaces of the pattern corresponding to the surface against which the aluminum body described above is to be cast are coated with a film 12 of a lightly sticky, moderately viscous material such as a relatively light lubricating oil. Next, a plurality of porous, generally spherical plastic particles or beads 14 are dispersed over the oil coating :12. The beads adhere lightly to the pattern surface through the medium of the oil film. Alternatively, the oil-coated pattern may be rolled in a loose FIGURE 1 having a beads adhering to the outer mass of the beads as a consequence of which a relatively I a dense layer of the plastic beads is picked up, so to speak, and retained on the oiled surface. Preferably the beads are applied with sufiicient density so that the pattern has a surface appearance generally akin to that of a pimpled surface, but that there is sufiicient space between the beads to permit molten metal to flow between them.

The coating 12 may be formed of any material which may be readily applied to the surface of the pattern and removed therefrom, and which will hold the light synthetic resin beads lightly on the pattern as above described and readily release them after the beads have been embedded in the sand mold. A wide variety of relatively viscous non-setting organic materials having an oily or greasy characteristic may be suitable for this purpose. Preferably, the coating is formed of oily materials such as hydrocarbon oils, vegetable oils, polymeric materials such as polyethylene glycol and similar glycols which are typically used as mold release agents and the like in {foundry procedures and which do not have an adverse eifect on the molds.

Expanded polystyrene beads have been found particularly suitable for use in the present invention. The expanded polystyrene beads referred to are the well known expandable polystyrene beads such as those which are sold by the Koppers Company and the Dow Chemical Company which have been expanded. These expandable polystyrene beads are polystyrene pellets or beads in which there is dissolved a relatively volatile material such as dichlorodiliuoromethane or heptane. When these expandable polystyrene beads are subjected to heat in the vicinity of about 330 F. to 450 F., the melting or softening range of the polystyrene material, the volatile material will expand as the polystyrene softens and cause the beads to expand or foam and form a porous or open-cell generally spherical structure. The expanded polystyrene beads employed in the present invention are formed by merely subjecting the commercially available expandable polystyrene beads to steam or heat in the vicinity of about 500 F. for a time sufficient to cause the beads to expand. Preferably, the expanded beads which are employed in the process are inch in diameter or greater for reasons to be made clear hereinafter. Rigid porous particles of other synthetic resins which, on coming in contact with a molten metal being cast such as aluminum will readily volatilize or burn out, may also be used.

After application of the beads 14 to the oil surface 12 of the pattern, the pattern is embedded in a sand mold which may consist of a drag 16 and cope 18 as shown in FIGURE 3. The conventional foundry green sand may be employed for this purpose although it will be apparcut that various foundry molding procedures may be employed.

Next, the pattern 10 is removed from the green sand mold as shown in FIGURE 4 with the result that the beads 14- are left embedded in the mold walls adjacent to the mold cavity 20 formed by the removal of the pattern 10 therefrom. As shown in FIGURE 3, the cope 18 is formed with a suitable core 22 for the purpose of providing a sprue and gating to the mold cavity 26.

Next, a ferrous metal suitable for use as a brake surface is poured into the mold through the sprue 22 into the mold cavity 20. As the mold cavity 20 is being filled, hot gases generated by the molten metal penetrate into the porous polystyrene beads 14 with the result that the polystyrene is volatilized and burned out. The molten metal fills the voids created by the volatilized plastic as shown in FIGURE 4. As a result of this casting process, a ferrous metal liner is formed as shown in FIGURE which consists of an annular flanged member 24 having a plurality of partially spherical projections or beads 26 preferably in close proximity to one another and integrally attached to the outer side thereof.

The beaded ferrous metal liner 24 is then positioned in the mold cavity of a second green sand mold consisting of a drag 28 and a cope 39 having a spr-ue 32 therein. In place of a green sand mold, a ferrous metal permanent mold or other suitable mold may be employed. Molten aluminum is then cast about the liner 24 to form a brake drum thereabout. The molten aluminum flows about each of the beads 26 of the ferrous metal liner whereby a strong mechanical joint is formed between each ferrous metal bead and the aluminum brake drum as shown in FlGURE 7. As indicated above, the beads are formed a sufficient distance apart to insure that the molten aluminum will flow about each ferrous metal bead and thereby provide a maximum interlocking of the aluminum body with the ferrous metal body.

The polystyrene beads are preferably in excess of of an inch and of a generally spherical configuration so that the ferrous metal projections 26 are in effect balls integrally attached to the liner 24. These balls are in effect projections having enlarged extremities. When the aluminum body is cast about these projections so that the molten aluminum flows about them, an interlocking between the ferrous and aluminum bodies is an effect which may not be broken without shearing the beads from the ferrous liner. It has been found that the polystyrene beads should be at least of an inch in diameter or greater to insure that sufficient space is provided on the under side of the ferrous metal beads 26 to permit free flow of metal thereto under gravity casting conditions. In the event that pressure casting methods are employed, beads having a diameter of less than A inch may be used.

The brake drum 34 may be cast about the liner 24 by any suitable means including sand-type molds and permanent molds as well as by means of die casting techniques.

Although as described above, the method of this invention has particular utility in forming composite articles of a ferrous metal or a light metal such as aluminum or magnesium, it is obvious that it may be readily employed to cast composite articles of any metals having markedly different melting points.

The term aluminum as used herein is means to include alloys of aluminum such as, for example, alloys containing in the neighborhood of by weight, aluminum or more and alloys of aluminum which have physical properties typically associated with aluminum. Similarly, the terms magnesium and ferrous metal are intended to include alloys containing these elements as principal constituents.

While the invention has been described in terms of specific examples, it is to be understood that the scope of the invention is not limited thereby except as defined in the following claims.

We claim:

1. A method of making a composite article formed of at least first and second different metal portions comprising the steps of providing a pattern, applying an adherent liquid film over a surface of said pattern, dispersing a plurality of porous plastic substantially spherical beads over said liquid film whereby said beads are caused to adhere lightly to said pattern, forming a foundry sand mold over the beaded surface of said pattern, removing said pattern from said mold whereby said beads are embedded in a wall of said mold, casting said first metal against said wall whereby said first metal burns out and displaces said porous plastic beads to for-m said first metal portion having a beaded surface, said beaded surface comprising partially substantially spherical beads of said first metal, removing said mold from the casting, and finally casting said second metal portion over said beaded surface.

2. A method of making a composite article formed of a ferrous metal portion and a light metal portion having a melting point substantially less than the ferrous metal portion comprising the steps of providing a pattern, applying an oily film over a surface of said pattern, dispersing a plurality of porous substantially spherical plas-tic beads over said oily film whereby said beads are caused to adhere lightly to said pattern, forming a foundry sand mold over the beaded surface of said pattern, removing said pattern from said mold whereby said beads are embedded in a wall of said mold, casting ferrous metal against said wall whereby the ferrous metal burns out and displaces said porous plastic beads and said ferrous metal portion having a partially substantially spherical beaded surface is formed, removing said mold from said ferrous metal portion, and casting said light metal portion over said beaded surface.

3. A method of making a composite article formed of a ferrous metal portion and an aluminum portion comprising the steps of providing a pattern, applying an oily film over a surface of said pattern, dispersing a plurality of porous substantially spherical polystyrene beads over said oily film whereby said beads are caused to adhere lightly to said pattern, forming a foundry sand mold over the beaded surface of said pattern, removing said pattern from said mold whereby said beads are embedded in a wall of said mold, casting a ferrous metal member against said wall whereby the ferrous metal burns out and displaces said porous polystyrene beads to form said ferrous metal portion having a partially substantially spherical beaded surface, removing said mold from said ferrous metal portion, and finally casting said aluminum portion over said beaded surface.

4. A method of making a metal casting having a plurality of projections on the surface thereof comprising the steps of providing a pattern, applying an adherent liquid film over a surface of said pattern, dispersing a plurality of porous substantially spherical plastic beads over said film whereby said beads are caused to adhere lightly to said pattern, forming a foundry sand mold over the beaded surface of said pattern, removing said pattern from said mold whereby said beads are embedded in a wall of said mold, casting said metal against said wall whereby the molten metal burns out and displaces said porous plastic beads to form a metal casting having a partially substantially spherical beaded surface, and re moving said mold from the resulting metal casting.

5. A method of making a ferrous metal casting having a plurality of projections on a surface thereof comprising the steps of providing a pattern, applying an oily film over a surface of said pattern, dispersing a plurality of porous substantially spherical polystyrene beads over said oily film whereby said beads are caused to adhere lightly to said pattern, forming a foundry sand mold over the beaded surface of said pattern, removing said pattern from said mold whereby said beads are embedded in a wall of said mold, casting ferrous metal against said wall whereby the molten ferrous metal burns out said porous polystyrene beads to form a ferrous metal casting having a partially substantially spherical beaded surface, and removing said mold from the resulting ferrous met-a1 casting.

6. A method of making a composite brake drum assembly comprising a ferrous metal liner and an aluminum drum comprising the steps of providing a pattern of the said liner, applying an adherent liquid film over the outer surface of said pattern, dispersing a plurality of porous substantially spherical polystyrene beads over said film whereby said beads are caused to adhere lightly to the outer surface of said pattern, forming a foundry sand mold about said pattern, removing said pattern from said mold whereby said beads are embedded in a wall of the mold cavity of said mold, casting a ferrous metal member against said wall whereby the ferrous metal burns out and displaces said porous plastic beads to form a ferrous liner having a partially substantially spherical beaded surface, removing said mold from the resulting ferrous metal casting, and finally casting an aluminum drum over said beaded surface.

7. A method of making a composite article comprising a ferrous metal liner and an aluminum body cast therearoun-d comprising the steps of providing a pattern of the said liner, applying an adherent liquid film over the outer surface of said pattern, dispersing a plurality of porous substantially spherical plastic beads over said film whereby said beads are caused to adhere lightly to the outer surface of said pattern, [forming a foundry sand mold about said pattern, removing said pattern from said mold whereby said beads are embedded in a wall of the mold cavity of said mold, casting a ferrous metal in said cavity where-by the ferrous metal burns out and displaces said porous plastic beads to form a ferrous liner having a beaded outer surface, removing said mold from the resulting ferrous metal casting, and finally casting an aluminum body over said beaded surface.

8. A method of making a composite article comprising a ferrous metal liner and an aluminum body cast therearound comprising the steps of providing a pattern of the said liner, applying an adherent liquid film over the outer surface of said pattern, dispersing a plurality of porous plastic generally spherical beads over said film whereby said beads are 'caused to adhere lightly to the outer surface of said pattern, forming a foundry sand mold about said pattern, removing said pattern from said mold whereby said beads are embedded in a wall of the mold cavity of said mold, casting a ferrous metal within said cavity whereby the ferrous metal displaces said porous plastic beads to form a ferrous liner having beads having enlarged end portions on a surface thereof, removing said mold from the resulting ferrous metal casting, and finally casting an aluminum body over said beaded surface whereby cast aluminum is formed about said beads in positive interlocking relation.

References Cited in the file of this patent UNITED STATES PATENTS 1,553,670 Cautley Sept. 15, 1925 1,676,976 Angle et a1 July 10, 1928 2,366,262 Hollerith Jan. 2, 1945 2,398,501 Le Jeune Apr. 16, 1946 2,830,343 Shroyer Apr. 15, 1958 2,836,867 Bean June 3, 1958 OTHER REFERENCES Light Metal Age, April 1960, pp. 15 and 33. 

1. A METHOD OF MAKING A COMPOSITE ARTICLE FORMED OF AT LEAST FIRST AND SECOND DIFFERENT METAL PORTIONS COMPRISING THE STEPS OF PROVIDING A PATTERN, APPLYING AN ADHERENT LIQUID FILM OVER A SURFACE OF SAID PATTERN, DISPERSING A PLURALITY OF POROUS PLASTIC SUBSTANTIALLY SPHERICAL BEADS OVER SAID LIQUID FILM WHEREBY SAID BEADS ARE CAUSED TO ADHERE LIGHTLY TO SAID PATTERN, FORMING A FOUNDARY SAND MOLD OVER THE BEADED SURFACE OF SAID PATTERN, REMOVING SAID PATTERN FROM SAID MOLD WHEREBY SAID BEADS ARE EMBEDDED IN A WALL OF SAID MOLD, CATING SAID FIRST METAL AGAINST SAID WALL WHEREBY SAID FIRST METAL BURNS OUT AND DISPLACES SAID POROUS PLASTIC BEADS TO FORM SAID FIRST METAL PORTION HAVING A BEADED SURFACE, SAID BEADED SURFACE COMPRISING PARTIALLY SUBSTANTIALLY SPHERICAL BEADS OF SAID FIRST METAL, REMOVING SAID MOLD FROM THE CASTING, AND FINALLY CASTING SAID SECOND METAL PORTION OVER SAID BEADED SURFACE. 